Classification of developmental hip dysplasia
There are 2 main classifications of developmental hip dysplasia in adult hip surgery as follows.
I. Crowe’s classification method
Crowe et al. classified it into 4 types according to the ratio of the distance of femoral head displacement to the height of the femoral head and pelvis measured by X-rays.
Type I: femoral head displacement accounting for less than 50% of the femoral head height or less than 10% of the pelvic height
Type II: femoral head displacement of 50-75% of the femoral head height or 10%-15% of the pelvic height
Type III: femoral head displacement of 75%-100% of the femoral head height or 15%-20% of the pelvic height
Type IV: femoral head displacement exceeding 100% of the femoral head height or 20% of the pelvic height.
II. Hartofilakidis classification
Hartofilakidis et al. classified DDH into 3 types according to the degree of dislocation of the femoral head.
Type I: dysplasia/subluxation of the hip joint: that is, the hip joint is dysplastic or subluxated to varying degrees, and most of the femoral head is still contained within the true socket, but there is mostly shallowing of the acetabulum and bony defects on the upper edge of the acetabulum.
Type II: low hip dislocation: the femoral head is articulated with a pseudosocket on the iliac wing, there is an overlap area between the pseudosocket and the true socket, there are bone defects on the anterior and posterior walls of the acetabulum and the acetabulum is shallow with a small opening.
Type III: High hip dislocation: the femoral head is clearly displaced upward and backward and forms an articulation with a distinct, independent pseudomalleolus on the iliac wing, and there are bone defects on all four walls of the acetabulum.
The above two classifications are mainly used in patients who underwent hip arthroplasty due to DDH. Since the majority of patients with hip dysplasia requiring osteotomy have an upward displacement of the femoral head less than 50% of the height of the femoral head, the Crowe classification has no practical significance. The Hartofilakidis classification of type II and III is a complete dislocation, and the type I classification is rough and does not apply to the classification of hip preservation patients.
Karl Perner DDH classification
This classification divides DDH into 4 degrees.
Degree I: mild, with mild incomplete coverage of the femoral head by the acetabulum, with the femoral head still located in the center of the hip joint and a CE angle between 11° and 35°.
II degree: moderate, the femoral head is still located in the center of the hip joint, with a CE angle between 0° and 10°.
III degree: severe, with the head of the femur dislocated upward and laterally, the acetabulum flattened, and a negative CE angle
IV degree: complete hip dislocation with the femoral head located outside the acetabulum.
The Karl Perner classification provides a clear classification of simple hip dysplasia and hip subluxation and is applicable to the selection and evaluation of patients for hip preservation surgery.